Domestic humidifying apparatus is generally in the form of a portable appliance having a casing comprising a water tank for storing a volume of water, and a fan for creating a flow of air through an air duct of the casing. The stored water is conveyed, usually under gravity, to an atomizing device for producing water droplets from the received water. This device may be in the form of high frequency vibrating device, such as a transducer. The water droplets enter the flow of air passing through the air duct, resulting in the emission of a mist into the environment. The appliance may include a sensor for detecting the relative humidity of the air in the environment. The sensor outputs a signal indicative of the detected relative humidity to a drive circuit, which controls the transducer to maintain the relative humidity of the air in the environment around a desired level. Typically, the actuation of the transducer is stopped when the detected relative humidity is around 5% higher than the desired level, and is restarted when the detected relative humidity is around 5% lower than the desired level.
The flow rate of the air emitted from such a humidifier tends to be relatively low, for example in the range from 1 to 2 litres per second, and so the rate at which the humid air is dispersed into a room can be very low. Furthermore, as the relative humidity of the air in the local environment of the humidifier will rise relatively rapidly in comparison to that of the air in the local environment of the user, the relative humidity detected by the sensor will not, at least initially, be indicative of the relative humidity of the air local to the user. As a result, the actuation of the transducer may be stopped when the relative humidity of the air in the local environment of the user is significantly below the desired level. Due to the relative low rate at which the humid air is dispersed into the room, it can then take some time for the detected relative humidity to fall to a level at which the actuation of the transducer is restarted. Consequently, it may take a long period of time for the relative humidity of the air in the local environment of the user to reach the desired level.